Schistosomes

Question 1

Q: What class are schistosomes?

Answer 1

Parasitic Helminths > Flatworms > Flukes > Schistosomes (cutaneous penetration rather than oral ingestion)

Question 2

Direct host?

Indirect host?

Answer 2

1. Humans
2. Snails

Question 3

Label the eggs

Answer 3

Question 4

Which snail carries which Schistosome?

Answer 4

Question 5

What are the adult locations in the host?

Answer 5

• S. mansoni: typically in mesenteric veins draining the large intestine and posterior segment of the ileum.
• S. japonicum: typically in branches of the mesenteric vein draining the small intestine
• S. haematobium: small venules of the vesical plexus and pelvic plexus and sometimes also the rectal venules.
• The adult females produce eggs in these locations.
• To complete the life cycle eggs pass through the gut/bladder wall into the faeces/urine and out into the environment.

Question 6

Label the adult

Answer 6

Question 7

What are the names of the different stages?

Answer 7

1. Eggs hatch in water after contaminated by infected faeces or urine;
2. Miracidium released + enter the snails.
3. Sporocysts develop in the snails. (Mother> Mantle, Daughter Digestive; cecarae from daughter)
4. Cecarae are released from snail in response to light
5. Cecarae enter through exposed skin, shedding their tails and become
6. Schistosomules, which travel in the blood to the liver where they mature into adult
7. Shistosomes, which pair up and being producing eggs, 50% of which esacpe and continue the cycle, the other 50% of which accumulate in tissues causing pathology.

Question 8

Name and clinical presentation of acute schistosomiasis?

Answer 8

“KATAYAMA fever”

3-8 weeks post infection (onset of egg production). Up to 90% prevalence following first exposure, more unusual in endemic settings.

Symptoms may include: Malaise, low grade fever § Head/neck ache § Urticaria

Eosinophilia, Hepatomegaly, splenomegaly, Diarrhoea, Cough and wheeze

Aetiology uncertain - but probably mediated by immune complexes of soluble worm or egg antigens and antibody (hypersensitivity reaction).

Question 9

CHRONIC SCHISTOSOMIASIS

Answer 9

The main target of the parasite is to expel its ova to the external environment in order to maintain species survival

• Pathology in the host is due to the immune response to the EGGS stuck in tissues, as well as the damage caused by egg passage
• Primary targets:
  • Liver and intestines: S. mansoni, S. japonicum, S. mekongi,
• S. intercalatum
  • Urinary bladder and ureters: S. haematobium
• Secondary targets: “Ectopic schisto” (lungs, CNS, genital tract)

Question 10

What are the clinical manifestations of Mansoni & Japonicum?

Answer 10

HEPATOSPLENIC schistosomiasis

• Eggs trapped in the presinusoidal vessels of the liver • The granulomatous response, fibrosis and calcification, causes periportal fibrosis (severe in 5-10% of patients):
• Blockage of blood flow in liver → • portal hypertension • hepatosplenomegaly • ascites

INTESTINAL SCHISTOSOMIASIS:

Passage of eggs →ulceration → haemorrhage

Mucosal thickening and inflammatory polyps may cause obstruction